On the mower's eighth run across the park, Uetaha stopped running behind the mower and sat down while the other two children continued to chase the mower.
On the ninth run, the mower passed the boy as he sat on the ground. During the 10th run, Uetaha was running at a diagonal angle towards the tractor when he was struck and run over by the right-hand side of the mower unit.
Judge Rea said the tragedy occurred because the council's "informal rules" for dealing with such situations were not being followed at the time.
The judge said that while the council "in all ways except this one occasion" had systems in place to protect its staff and the public, it "fell below the required standard" by not appropriately identifying risks to children from its mower operations.
"They did not have clear and unambiguous guidance to their staff as to procedures that should be followed when children were at risk during these operations."
The council had already paid $12,356 in reparations to Uetaha's family, which was not part of the sum it was ordered to pay yesterday.
Acting chief executive John O'Shaughnessy, who was in court for the sentencing yesterday, said the council was "devastated by the tragedy and deeply regret the loss suffered by Uetaha's whanau".
The council had apologised to the family for its role in the tragedy and repeated that apology in court yesterday.
"We acknowledge that we could and should have done more to make sure one of our precious little residents was safe," Mr O'Shaughnessy said.
"Staff have been working hard since the day of the loss of Uetaha to ensure procedures are in place to make sure a tragedy like this never happens again.
"Our standard operating procedures have been changed and will continue to be updated to deal with any risks. Staff have received full training on the new procedures."
Hastings Mayor Lawrence Yule said the "horrendous" accident had had a huge impact on the council and was the only incident he was aware of where the council's operations had led to a child's death.
"[The sentencing] doesn't bring the little boy back, it doesn't help with the distress that it's caused to a very good employee of ours, but it does bring to an end the court processes that are followed after such a tragic incident."
WorkSafe chief inspector Keith Stewart said children were at particular risk when public areas such as parks were being mown.
Mr Stewart said the council's informal system of stopping the mower and not starting it again until a member of the public had moved on should have been formalised and documented.
"The guidance should also have been clearly articulated to all staff so that they knew how to use the tractor mowers safely.
"Those simple steps could have made all the difference to the victim and his family."
The council pleaded guilty in February to breaching the Health and Safety in Employment Act in relation to the incident.
Last year, Ross David Pollock, the driver of the tractor, pleaded guilty to driving a vehicle dangerously.
On July 11, he was sentenced to six months' home detention, 100 hours' community work, disqualified from driving for three years and ordered to pay $5000 reparation. Pollock later appealed the driving disqualification period, which was reduced to 18 months.
